131 



by countins: (ho colloctions of oroanisius that arc c'aii<iht and dcvd- 

 oped oil appropriate i>lass phites prepared aoeordiiig to tlie iiietliods 

 of Miqiiel at Moiitsouris. Their observations show that in JM) cases 

 out of 40 the catch of trorins within the forest is less than the catch 

 outside the forest, the average ratio being as 3 to 1. so that the forests 

 act as a strainer upon the organisms carried by the wind. WoUny 

 suggests that the result Avould be even still more decided if the wind 

 were stronger and the forests more extensive. (Wollny, Forschun- 

 gen, 1891, XIV, p. 176.) 



ATMOSPHERIC ELECTRICITY. 



IN GENERAL. 



The relations of atmospheric electricity to vegetation and crops 

 are too little understood to justify any attempt to present this sub- 

 ject. In fact, it does not seem clear that any appreciable influence 

 is exerted by this atmospheric or geophysical element upon the 

 development of plants. In natural conditions evaporation is un- 

 doubtedly facilitated by the dissipation of an electric charge, but 

 we do not know that transpiration is at all affected by it, and have 

 no reason to think that assimilation is affected by it. The passage 

 of an electric current through the earth in proximity to the roots 

 may affect the decomposition of the soil and setting free of nutritious 

 substances or may affect the temperature of the soil. A fcAv experi- 

 ments have been made to show that artificial earth currents stimulate 

 the growth of the plant, but. nothing has yet been found to show that 

 under natural conditions electric currents have any appreciable 

 influence. Nevertheless, observations are made regularly at some 

 stations, such as Kew, JNIontsouris, Potsdam, and at a few agricul- 

 tural experiment stations. 



An excellent series was maintained for many years by AVisliczenus 

 at St. Louis, Mo., a summary of Avhich is published in the transac- 

 tions of the Academy of Science at St. Louis and also at page 65, 

 Report of the Chief Signal Officer for 1871. The following table 

 gives the monthly means for Montsouris and for St. Louis. The 

 record for Montsouris expresses the potential in units of 1 Daniell 

 cell, which is approximately 1 volt at a point 2 meters above the 

 soil and 1 meter from a Avail, for the calm days of the years 1880 to 

 1887. The record for St. Louis gives the electric intensity on a scale 



